Ruthenium complex and photoelectric component using the same

ABSTRACT

The present invention relates to a ruthenium complex represented by the following formula (I): 
       RuL 2 (NCS) 2 A m    (I)         wherein L, A and m are defined the same as the specification, and a photoelectric component using the same. The ruthenium complex of the present invention can be used in a Dye-Sensitized Solar Cell (DSSC). Hence, the photoelectric characteristics of the DSSC manufactured with the ruthenium complex of the present invention can be improved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a ruthenium complex and a photoelectriccomponent using the same and, more particularly, to a ruthenium complex,which is used for the dye-sensitized solar cell (DSSC), and aphotoelectric component using the same.

2. Description of Related Art

With the development of industrial technology, the serious problems thatthe whole world is facing today are the energy crisis and theenvironmental pollution. In order to solve the global energy crisis andto reduce the environmental pollution, one of the effective means is thesolar cell, which can convert the solar energy into the electricity.Since the dye-sensitized solar cell has the advantages of lowmanufacturing cost, large-scale production, great flexibility, lighttransmittance, and being capable of use in the buildings, theapplication of the dye-sensitized solar cell becomes more and moreattractive.

Currently, Grätzel et al. have disclosed a series of literatures, forexample, O'Regan, B.; Grätzel, M. Nature 1991, 353, 737, which shows thepracticability of the dye-sensitized solar cell. The general structureof the dye-sensitized solar cell comprises an anode, a cathode, anano-porous titanium dioxide layer, a dye, and electrolyte, wherein thedye plays a critical role in the conversion efficiency of thedye-sensitized solar cell. The dye suitable for the dye-sensitized solarcell must have characteristics in broad absorption spectrum, high molarabsorption coefficient, thermal stability, and light stability.

Grätzel's lab has published a serious of ruthenium complexes as the dyesfor the dye-sensitized solar cell. Grätzel's lab published adye-sensitized solar cell prepared with a N3 dye in 1993, and theconversion efficiency of the dye-sensitized solar cell is 10.0% underthe illumination of AM 1.5 stimulated light. The incidentphoton-to-current conversion efficiency (IPCE) value of the N3 dye is80% in the range of 400 to 600 nm. Although hundreds of dye complexeshave developed, the conversion efficiency of those dye complexes is notas good as that of the N3 dye. The structure of the N3 dye isrepresented by the following formula (a).

In 2003, Grätzel's lab published a dye-sensitized solar cell preparedwith a N719 dye, and the conversion efficiency of the dye-sensitizedsolar cell is improved to 10.85% under the illumination of AM 1.5stimulated light, wherein the structure of the N719 dye is representedby the following formula (b).

Grätzel's lab also published a dye-sensitized solar cell prepared with ablack dye in 2004, and the conversion efficiency of the dye-sensitizedsolar cell is 11.04% under the illumination of AM 1.5 stimulated light.The black dye can enhance the spectral response in red and near-IRregion, so the conversion efficiency of the dye-sensitized solar cellcan be improved. The structure of the black dye is represented by thefollowing formula (c).

In addition to the ruthenium complexes such as the N3 dye, the N719 dye,and the black dye, other types of dye compounds, which can be used inthe dye-sensitized solar cell, are platinum complexes, osmium complexes,iron complexes, and copper complexes. However, the results of variousresearches show that the conversion efficiency of the rutheniumcomplexes is still better than other types of dye compounds.

The dyes for the dye-sensitized solar cell influence the conversionefficiency greatly. Hence, it is desirable to provide a dye compound,which can improve the conversion efficiency of the dye-sensitized solarcell.

SUMMARY OF THE INVENTION

The present invention is to provide a novel ruthenium complex, which isused for a dye-sensitized solar cell to improve the photoelectricefficiency of the dye-sensitized solar cell.

The present invention is also to provide a dye-sensitized solar cell,which has excellent photoelectric property.

Hence, the present invention provides a ruthenium complex, which isrepresented by the following formula (I):

RuL₂(NCS)₂A_(m)   (I)

wherein

-   L is 2,2′-bipyridyl-4,4′-dicarboxylic acid,    2,2′-bipyridyl-4,4′-disulfonic acid, or    2,2′-bipyridyl-4,4′-diphosphonic acid;-   A is a quaternary phosphonium cation; and-   m is 1, 2, 3, or 4.

In the above formula (I), L can be 2,2′-bipyridyl-4,4′-dicarboxylicacid, 2,2′-bipyridyl-4,4′-disulfonic acid, or2,2′-bipyridyl-4,4′-diphosphonic acid. Preferably, L is2,2′-bipyridyl-4,4′-dicarboxylic acid.

In the above formula (I), A may be a quaternary phosphonium cation.Preferably, A is P⁺R₁R₂R₃R₄, wherein R₁, R₂, R₃, and R₄ are eachindependently C_(1˜20) alkyl, phenyl, or benzyl. More preferably, A istetraalkylphosphonium, benzyl trialkylphosphonium, or phenyltrialkylphosphonium, and the alkyl is C_(1˜20) alkyl.

In the above formula (I), m may be 1, 2, 3, or 4. Preferably, m is 2, or3. More preferably, m is 2.

The specific examples of ruthenium complex represented by the aboveformula (I) are:

The present invention provides a dye-sensitized solar cell, whichcomprises the aforementioned ruthenium complex.

In addition, the dye-sensitized solar cell of the present inventioncomprises: a photoanode comprising the aforementioned ruthenium complex;a cathode; and an electrolyte layer disposed between the photoanode andthe cathode.

In the dye-sensitized solar cell of the present invention, thephotoanode comprises: a transparent substrate, a transparent conductivelayer, a porous semiconductive layer, and a dye of the rutheniumcomplex.

In the dye-sensitized solar cell of the present invention, the materialof the transparent substrate is not particularly limited, as long as thematerial of the substrate is a transparent material. Preferably, thematerial of the transparent substrate is a transparent material withgood moisture resistance, solvent resistance and weather resistance.Thus, the dye-sensitized solar cell can resist moisture or gas fromoutsides by the transparent substrate. The specific examples of thetransparent substrate include, but are not limited to, transparentinorganic substrates, such as quartz and glass; transparent plasticsubstrates, such as poly(ethylene terephthalate) (PET), poly(ethylene2,6-naphthalate) (PEN), polycarbonate (PC), polyethylene (PE),polypropylene (PP), and polyimide (PI). Additionally, the thickness ofthe transparent substrate is not particularly limited, and can bechanged according to the transmittance and the demands for theproperties of the dye-sensitized solar cell. Preferably, the material ofthe transparent substrate is glass.

Furthermore, in the dye-sensitized solar cell of the present invention,the material of the transparent conductive layer can be indium tin oxide(ITO), fluorine-doped tin oxide (FTO), ZnO—Ga₂O₃, ZnO—Al₂O₃, ortin-based oxides.

In addition, in the dye-sensitized solar cell of the present invention,the porous semiconductive layer is made of semiconductor particles.Suitable semiconductor particles may include Si, TiO₂, SnO₂, ZnO, WO₃,Nb₂O₅, TiSrO₃, and the combination thereof. Preferably, thesemiconductor particles are made from TiO₂. The average diameter of thesemiconductor particles may be 5 to 500 nm. Preferably, the averagediameter of the semiconductor particles is 10 to 50 nm. Furthermore, thethickness of the porous semiconductive layer is 5-25 μm.

In the dye-sensitized solar cell of the present invention, the rutheniumcomplex may be the aforementioned ruthenium complex.

Besides, the material of the cathode for the dye-sensitized solar cellis not particularly limited, and may include any material withconductivity. Otherwise, the material of the cathode can be aninsulating material, as long as there is a conductive layer formed onthe surface of the cathode, wherein the surface of the cathode is facedto the photoanode. The material of the cathode can be a material withelectrochemical stability. The unlimited examples suitable for thematerial of the cathode include Pt, Au, C, or the like.

Furthermore, the material used in the electrolyte layer of thedye-sensitized solar cell is not particularly limited, and can be anymaterial, which can transfer electrons and/or holes.

Other objects, advantages, and novel features of the invention willbecome more apparent from the following detailed description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The ruthenium complex of the present invention can be synthesized by thefollowing methods.

cis-di(thiocyanato)-N,N′-bis(2,2′-bipyridyl-4,4′-dicarboxylicacid)ruthenium(II) (N3 dye) is synthesized according to the methoddescribed in Inorganic Chemistry, Vol. 38, No. 26, 1999, 6298-6305.

cis-di(thiocyanato)-N,N′-bis(2,2′-bipyridyl-4,4 ′-dicarboxylicacid)ruthenium(II) is dissolved in distilled water, and 10% aqueoussolution of tetrabutylphosphonium hydroxide reagent (TCI Co. Ltd.) isadded thereto to adjust the pH value of the reaction solution to 11.Then, the reaction solution is concentrated to obtain a viscous liquid.The viscous liquid is dissolved in methanol, and the diethyl ether isadded thereto to precipitate a product. After the wet solid product istaken out and dried under vacuum for 1 day, the dried solid product isdissolved in distilled water, and then the pH value of the resultedsolution is adjusted below 5 with 0.1 M nitric acid_((aq)). Finally, theruthenium complex of formula (I-1) is obtained.

The method for manufacturing the dye-sensitized solar cell of thepresent invention is not particularly limited, and the dye-sensitizedsolar cell of the present invention can be manufacture by the knownmethods in the art.

The material of the transparent substrate is not particularly limited,as long as the material of the substrate is a transparent material.Preferably, the material of the transparent substrate is a transparentmaterial with good moisture resistance, solvent resistance and weatherresistance. Thus, the dye-sensitized solar cell can resist moisture orgas from outsides by the transparent substrate. The specific examples ofthe transparent substrate include, but are not limited to, transparentinorganic substrates, such as quartz and glass; transparent plasticsubstrates, such as poly(ethylene terephthalate) (PET), poly(ethylene2,6-naphthalate) (PEN), polycarbonate (PC), polyethylene (PE),polypropylene (PP), and polyimide (PI). Additionally, the thickness ofthe transparent substrate is not particularly limited, and can bechanged according to the transmittance and the demands for theproperties of the dye-sensitized solar cell. In a specific embodiment,the material of the transparent substrate is a glass substrate.

Furthermore, the material of the transparent conductive layer can beindium tin oxide (ITO), fluorine-doped tin oxide (FTO), ZnO—Ga₂O₃,ZnO—Al₂O₃, or tin-based oxides. In a specific embodiment, fluorine-dopedtin oxide is used for the transparent conductive layer.

In addition, the porous semiconductive layer is made of semiconductorparticles. Suitable semiconductor particles may include Si, TiO₂, SnO₂,ZnO, WO₃, Nb₂O₅, TiSrO₃, and the combination thereof. First, thesemiconductor particles are prepared in a form of paste, and then thepaste is coated on the transparent conductive substrate. The coatingmethod used herein can be blade coating, spin coating, spry coating, orwetting coating. Additionally, the coating can be held for one time ormany times, in order to obtain a porous semiconductive layer withsuitable thickness. The semiconductive layer can be a single layer ormultiple layers, wherein each layer of the multiple layers is formed bysemiconductor particles with different diameters. For example, thesemiconductor particles with diameters of 5 to 50 nm is coated in athickness of 5 to 20 μm, and then the semiconductor particles withdiameters of 200 to 400 nm is coated in a thickness of 3 to 5 μmthereon. After drying the coated substrate under 50-100° C., the coatedsubstrate is sintered under 400-500° C. for 30 min to obtain amultilayer semiconductive layer.

The ruthenium complex can be dissolved in a suitable solvent to preparea dye solution. Suitable solvents include, but are not limited to,acetonitrile, methanol, ethanol, propanol, butanol, dimethyl formamide,N-methyl-2-pyrrolidinone, and the combination thereof. Herein, thetransparent substrate coated with the semiconductive layer is dippedinto a dye solution to make the semiconductive layer absorb the dye inthe dye solution completely. After the dye absorption is completed, thetransparent substrate coated with the semiconductive layer is taken outand dried. Finally, a photoanode for a dye-sensitized solar cell isobtained.

Besides, the material of the cathode for the dye-sensitized solar cellis not particularly limited, and may include any material withconductivity. Otherwise, the material of the cathode can be aninsulating material, as long as there is a conductive layer formed onthe surface of the cathode, wherein the surface of the cathode is facedto the photoanode. The material of the cathode can be a material withelectrochemical stability. The unlimited examples suitable for thematerial of the cathode include Pt, Au, C, or the like.

Furthermore, the material used in the electrolyte layer of thedye-sensitized solar cell is not particularly limited, and can be anymaterial, which can transfer electrons and/or holes. In addition, theliquid electrolyte can be a solution of acetonitrile containing iodine,a solution of N-methyl-2-pyrrolidinone containing iodine, or a solutionof 3-methoxy propionitrile containing iodine. In a specific embodiment,the liquid electrolyte can be a solution of acetonitrile containingiodine.

One specific method for manufacturing the dye-sensitized solar cell ofthe present invention is presented as follow.

First, a paste containing TiO₂ particles with diameter of 20˜30 nm iscoated on a glass substrate covered with fluorine-doped tin oxide (FTO)for one time or several times. Then, the coated glass substrate issintered under 450° C. for 30 min.

The ruthenium complex is dissolved in a mixture of acetonitrile andt-butanol (1:1 v/v) to formulate a dye solution of ruthenium complex.Then, the aforementioned glass substrate with porous TiO₂ layer isdipped into the dye solution. After the porous TiO₂ layer absorbs thedye in the dye solution, the resulted glass substrate is taken out anddried. Finally, a photoanode is obtained.

A glass substrate covered with fluorine-doped tin oxide is drilled toform an inlet with a diameter of 0.75 μm, wherein the inlet is used forinjecting the electrolyte. Then, a solution of H₂PtCl₆ is coated on theglass substrate covered with fluorine-doped tin oxide, and the glasssubstrate is heated to 400° C. for 15 min to obtain a cathode.

Sequentially, a thermoplastic polymer layer with a thickness of 60 μm isdisposed between the photoanode and the cathode. These two electrodesare pressed under 120 to 140° C. to adhere with each other.

Then, an electrolyte is injected, wherein the electrolyte is a solutionof acetonitrile containing 0.03 M I₂/0.3 M LiI/0.5 M t-butyl-pyridine.After the inlet is sealed with thermoplastic polymer layer, adye-sensitized solar cell of the present invention is obtained.

The following examples are intended for the purpose of illustration ofthe present invention. However, the scope of the present inventionshould be defined as the claims appended hereto, and the followingexamples should not be construed as in any way limiting the scope of thepresent invention. Without specific explanations, the unit of the partsand percentages used in the examples is calculated by weight, and thetemperature is represented by Celsius degrees (° C.). The relationbetween the parts by weight and the parts by volume is just like therelation between kilogram and liter.

EXAMPLE 1 Synthesis ofcis-di(thiocyanato)-N,N′-bis(2,2′-bipyridyl-4,4′-dicarboxylicacid)ruthenium(II)bis(tetrabutyl phosphonium) (I-1)

0.50 part ofcis-di(thiocyanato)-N,N′-bis(2,2′-bipyridyl-4,4′-dicarboxylicacid)ruthenium(II) (N3 dye), which was prepared according to the methoddescribed in Inorganic Chemistry, Vol. 38, No. 26, 1999, 6298-6305, and10 parts of distilled water were added into a reaction flask, and thereaction solution was mixed and stirred. Then, 10% aqueous solution oftetrabutylphosphonium hydroxide reagent (TCI Co. Ltd.) was added intothe reaction solution drop by drop to adjust the pH value of thereaction solution to 11. The rotary-evaporator was used for removing thesolvent from the reaction solution to obtain a viscous liquid. Theviscous liquid was dissolved in methanol, diethyl ether was addedthereto to obtain a precipitate, and the wet solid precipitate was takenout and dried under vacuum for 1 day. The dried solid was dissolved in10 parts of distilled water, and 0.1 M nitric acid_((aq)) was used toadjust the pH value of the resulted solution below 5. The sintered glassfilter was used for filtering the product out, and 5 parts of distilledwater with pH 5 was used for washing the product. Finally, 0.39 part ofblack solid product (I-1) was obtained, and the yield of the product(I-1) was 75.9%.

EXAMPLE 2 Preparation of a Dye-Sensitized Solar Cell

A paste containing TiO₂ particles with diameter of 20˜30 nm was coatedon a glass substrate covered with fluorine-doped tin oxide (FTO) for onetime or several times, wherein the thickness of the glass substrate was4 mm and the electric resistance of the glass substrate is 10 Ω/□. Then,the coated glass substrate was sintered under 450° C. for 30 min, andthe thickness of the sintered porous TiO₂ layer was 10 to 12 μm.

The ruthenium complex prepared by Example 1 was dissolved in a mixtureof acetonitrile and t-butanol (1:1 v/v), and a dye solution containing0.5 mM ruthenium complex was prepared. Then, the aforementioned glasssubstrate covered with porous TiO₂ layer was dipped into the dyesolution to make the dye adhere on the porous TiO₂ layer. After 16 to 24hours, the resulted glass substrate was taken out and dried, and then aphotoanode was obtained.

A glass substrate covered with fluorine-doped tin oxide was drilled toform an inlet with a diameter of 0.75 μm, wherein the inlet was used forinjecting the electrolyte. Then, a solution of H₂PtCl₆ (2 mg Pt in 1 mlethanol) was coated on the glass substrate covered with fluorine-dopedtin oxide, and the resulted glass substrate was heated to 400° C. for 15min to obtain a cathode.

Sequentially, a thermoplastic polymer layer with a thickness of 60 μmwas disposed between the photoanode and the cathode. These twoelectrodes were pressed under 120 to 140° C. to adhere with each other.

Then, an electrolyte was injected, wherein the electrolyte was asolution of acetonitrile containing 0.03 M I₁/0.3 M LiI/0.5 Mt-butyl-pyridine. After the inlet was sealed with thermoplastic polymerlayer, a dye-sensitized solar cell of the present example was obtained.

COMPARATIVE EXAMPLE

The process for preparing the dye-sensitized solar cell of the presentcomparative example is the same as that described in Example 2, exceptthat the ruthenium complex prepared by Example 1 is substituted withN719.

Testing Methods and Results Test for the Photoelectric Characteristics

The short circuit current (J_(SC)), open circuit voltage (V_(OC)),filling factor (FF), photoelectric conversion efficiency (η), andincident photon-to-current conversion efficiency (IPCE) of thedye-sensitized solar cells prepared by Examples 2 and ComparativeExample were measured under the illumination of AM 1.5 stimulated light.The testing results are shown in the following Table 1:

TABLE 1 Testing results of the dye and the dye-sensitized solar cellJ_(SC) V_(OC) dye (mA/cm²) (V) FF η (%) Example 2 I-1 9.02 0.78 0.634.44 Comparative N719 7.36 0.76 0.61 3.38 Example

The resting results of Table 1 show that the short circuit current(J_(SC)), the open circuit voltage (V_(OC)) and the filling factor (FF)of the dye-sensitized solar cell prepared by the ruthenium complex ofthe present invention are improved, as compared with the dye-sensitizedsolar cell prepared by the N719 dye. It means that the ruthenium complexof the present invention can improve the photoelectric conversionefficiency of the dye-sensitized solar cell.

In conclusion, the present invention is different from the prior arts inseveral ways, such as in purposes, methods and efficiency, or even intechnology and research and design. Although the present invention hasbeen explained in relation to its preferred embodiment, it is to beunderstood that many other possible modifications and variations can bemade without departing from the scope of the invention as hereinafterclaimed. Hence, the scope of the present invention should be defined asthe claims appended hereto, and the foregoing examples should not beconstrued as in any way limiting the scope of the present invention.

1. A ruthenium complex, which is represented by the following formula(I):RuL₂(NCS)₂A_(m)   (I) wherein L is 2,2′-bipyridyl-4,4′-dicarboxylicacid, 2,2′-bipyridyl-4,4′-disulfonic acid, or2,2′-bipyridyl-4,4′-diphosphonic acid; A is a quaternary phosphoniumcation; and m is 1, 2, 3, or
 4. 2. The ruthenium complex as claimed inclaim 1, wherein L is 2,2′-bipyridyl-4,4′-dicarboxylic acid.
 3. Theruthenium complex as claimed in claim 1, wherein L is2,2′-bipyridyl-4,4′-disulfonic acid.
 4. The ruthenium complex as claimedin claim 1, wherein L is 2,2′-bipyridyl-4,4′-diphosphonic acid.
 5. Theruthenium complex as claimed in claim 1, wherein A is P⁺R₁R₂R₃R₄, andR₁, R₂, R₃, and R₄ are each independently C_(1˜20) alkyl, phenyl, orbenzyl.
 6. The ruthenium complex as claimed in claim 2, wherein A isP⁺R₁R₂R₃R₄, and R₁, R₂, R₃, and R₄ are each independently C_(1˜20)alkyl, phenyl, or benzyl.
 7. The ruthenium complex as claimed in claim2, wherein A is tetraalkylphosphonium, benzyl trialkylphosphonium, orphenyl trialkylphosphonium, and the alkyl is C_(1˜20) alkyl.
 8. Theruthenium complex as claimed in claim 2, wherein m is 2, 3, or
 4. 9. Theruthenium complex as claimed in claim 3, wherein A is P⁺R₁R₂R₃R₄, andR₁, R₂, R₃, and R₄ are each independently C_(1˜20) alkyl, phenyl, orbenzyl.
 10. The ruthenium complex as claimed in claim 3, wherein m is 2,or
 3. 11. The ruthenium complex as claimed in claim 4, wherein A isP⁺R₁R₂R₃R₄, and R₁, R₂, R₃, and R₄ are each independently C_(1˜20)alkyl, phenyl, or benzyl.
 12. The ruthenium complex as claimed in claim4, wherein m is 2, or
 3. 13. The ruthenium complex as claimed in claim1, wherein the ruthenium complex is a dye compound for a dye-sensitizedsolar cell.
 14. The ruthenium complex as claimed in claim 1, whereinformula (I) is the following formula (I-1), or (I-2):


15. The ruthenium complex as claimed in claim 14, wherein the rutheniumcomplex is a dye compound for a dye-sensitized solar cell.
 16. Adye-sensitized solar cell, comprising: (a) a photoanode, which comprisesa ruthenium complex represented by the following formula (I):RuL₂(NCS )₂A_(m)   (I) wherein L is 2,2′-bipyridyl-4,4′-dicarboxylicacid, 2,2′-bipyridyl-4,4′-disulfonic acid, or2,2′-bipyridyl-4,4′-diphosphonic acid; A is a quaternary phosphoniumcation; and m is 1, 2, 3, or 4; (b) a cathode; and (c) an electrolytelayer disposed between the photoanode and the cathode.
 17. A dyesolution, comprising: (A) a ruthenium complex represented by thefollowing formula (I), wherein the content of the ruthenium complex is0.01-1 wt %:RuL₂(NCS)₂A_(m)   (I) wherein L is 2,2′-bipyridyl-4,4′-dicarboxylicacid, 2,2′-bipyridyl-4,4′-disulfonic acid, or2,2′-bipyridyl-4,4′-diphosphonic acid; A is a quaternary phosphoniumcation; and m is 1, 2, 3, or 4; and (B) an organic solvent, wherein thecontent of the organic solvent is 99.99-99 wt %, and the organic solventis selected from the group consisting of acetonitrile, methanol,ethanol, propanol, butanol, dimethyl formamide, andN-methyl-2-pyrrolidinone.